The Challenge of Landing on Mars

The folks at NASA/JPL posted this amazing video to their YouTube channel today, highlighting the incredible engineering feat it will be to land the Curiosity Rover onto the surface of Mars. Because of Curiosity’s weight and size, the traditional “airbag” method isn’t going to cut it. Instead, Curiosity will be lowered gently to the surface of Mars via a rocket-propelled “skycrane”. It makes the landing even more complex and dangerous, and introduces a whole new level of risk into the landing. But once we get that SUV-sized rover crawling around the surface of Mars, all that risk will be totally worth it.

I’d also like to give NASA kudos in the production design of this feature. It really felt like I was watching a movie trailer, and not some dusty instructional video from a stodgy space agency. If NASA wants to inspire and educate, they hit the nail squarely on the head with this video. Okay, maybe it was a little over the top. I’m waiting to see a cameo from Batman, but still… nice work.

40 Responses

Was Neil Degrasse Tyson in any way involved in this? Coz I smell copious amounts of bad-ass in this video!!! 😀 [Disclaimer: I know NDT was probably not involved directly, but definitively approves.] I think I should start reading all the sci-fi I can get my hands on before real life makes it seem boring… This is awesome…

Fraser, Am I right that this landing methodology has not been tested on Earth perhaps due to different gravity, atmospheric conditions and costs? I’m sure it’s been computer modeled. There must be hundreds, if not more conditions, that, if not accounted for, will cause this landing to be a $2.5B (USD) loss…. Hope it goes well – a great and exciting mission indeed! Michael Mac Denver, CO

The article in Scientific American makes a point on how difficult it was to get a parachute that would work at supersonic speeds in the thin atmosphere of Mars. A lot of this probably has only been tested in a piecemeal fashion. It is going to be a big test for system integration.
LC

– Cruise stage to Mars is virtually identical with all missions since Viking, which probably built on earlier stages. See my link to “guided flight” above, it walks through some of the likenesses and differences:

– The clamshell, heat shields and planetary protection scheme are much like the Viking and later missions, except that the heat shield must be durable Apollo-like, because:

– The non-ballistic guided flight scheme to achieve the precision landing ellipse is new. Some of that has probably been tested; the weight use is not new IIRC.

– The Mars landing supersonic chutes were developed and rocket tested high in the atmosphere at great cost. That is why they stay with simply scaling them up when they must, and then tested for durability, open phase and so on only.

– The rocket descent including the engines I think are much like Viking, just moved to the sky crane. The difference is the crane maneuver. It has been extensively tested.

I so much LOVE to watch those videos coming from the NASA/JPL folks, that I can’t put it to words! They keep getting better and better! With videos like these, who wants to go to the movies to see some boring fantasy flick?? Ok, maybe I’m overstating, but this is the real deal folks, it’s not sci-fi! This video is a professional work of art, of a real life event!

Nice catch! It could be worse though – 20 meters of cable and 20 feet of distance.

Seriously, I think they know how to do it, but not how to solve the larger problem of making it understandable to the US public. They need a James Bond movie for that – anything fits into a JB car/suit/cell.

Oh, I’m all for it, I watched the movie prolly 10 times by now. Too much fun.

As for the parachutes, IIRC, they deploy them while doing 1000 MPH and cut them at 200 MPH. So 800 MPH delta-v, or 355 m/sec in normal units. Seems like very little bang for the buck. You can see SpaceX’s rationale for doing rockets-only

As a person working on the project, I thought I would clarify this statement to you.

The “skycrane” phase starts at ~20 m from the ground. At this altitude,
the rover is separated from the descent stage and lowered on three
bridles and an umbilical cord that connects the rover flight computer
with the descent stage. When the bridles are fully extended the rover
“hangs” at ~7 m from the descent stage. Something that may not be
obvious from watching the video is that the PDV (powered descent
vehicle, i.e, descent stage + rover) keeps decreasing in altitude until
the rover reaches the ground. At this time, the descent stage will be at
~5 m from the surface. Once touchdown has been declared (the rover
computer analyzes the thrust profile and looks for a persistent
signature of rover unloading), pyros are fired and the rover
bridles/umbilical cord are cut. Then two of the descent stage engines
are throttled down to induce a momentum which makes the descent stage
pitch over. Shortly after, all inboard engines are throttled up to 100%
thrust to move away from the landing site. This last phase is known as
“flyaway”.

It is actually clear in the video, (which again, is incredibly well made). The joke was that because of the infamous unit mixup of the Polar Lander, the mixed-unit description of altitude and tether length was an “uh oh” moment…

But, I can see how flight height AGL would be more natural in meters (part of navigation) and the physical length of an object would be in feet…

One thing I always wondered – is the cord able to retract/extend a few inches (cm!) in the last fraction of a second to provide ultra-fast response in the vertical direction, to help minimize the vertical velocity?

There is a mechanism called BUD (Bridle and Umbilical Device) that picks up the slack. The BUD retracts back the bridle/umbilical cord once touchdown has been declared. Let me know if you have any other questions.

No, what I mean is:
The rockets have a certain response time, which results in some vertical velocity on touch down. (clearly it can’t be absolutely zero, but there’s a desire to minimize it)

Imagine that the tether, even in its deployed state, has 12″ remaining wrapped around a spool, which has a controllable brake. (either on the rover or on the skycrane end) The retro-rockets now try to “land” the vehicle at a height of say 6″ above ground. The spool is then released, in a controlled way (but not requiring energy since it is only unspooling) to finish the landing.

This way, the requirements on the rocket system are reduced, which might be worth the added mechanism I described.

Apologies for the very late response. ~34 days from Mars! I checked with some of the mechanical/EDL folks and the complexity of the system you described would be undesirable (good thinking though). More importantly, descending with some vertical speed beyond the vertical velocity error (but not too much of it obviously) is a must since the touchdown sensor relies heavily on monitoring the throttle levels. We come down at a constant speed but we throttle down to ~50% once the rover is offloaded. If the vertical velocity is limited to the extra reelout, we may never declare touchdown.

Also a nice catch! I eyeballed the elevation charts in Wiki, and the MERs didn’t get so low but perhaps 1-2 km below MOLA instead of 3 km. Also, the non-ballistic descent will add distance (“S turns”; different angle of descent).

I dunno. I’ve yet to hear convincing reasons for the complicated sky-crane landing. They don’t want to kick up dust by going all the way to the surface on rockets? It seems like it would have been cheaper, weight-wise, to have a compressed gas apparatus to blow off the contamination. Which could have been used later for dust removal, too.
I guess the reason is ‘trust us; we know what we’re doing’. Maybe they do – I hope so. But it really seems that the engineers came up with this Rube Goldberg approach just because they could – just to ‘show off’. I REALLY hope it works.

There are more reasons: they save ~ 500 kg of mass, bumping up the mass from the 500 kg or so Vikings to the 1 mt MSL, by not covering it and using its legs as landing gear.

Any of those would have been enough.

You may get around the dust problem at great expense in mass. Blowing won’t help since the dust is already in the gear. (And famously, you can’t get Mars dust away with shaking or blowing anyway, see the Phoenix sampling problem and the solar panel issues.) But you can simply cover the rover as they have done earlier.

But the payload mass gain with the crane is, to my knowledge, the reason it was chosen.

But… but… if you can’t blow the dust off how come both Spirit and Oppotunity have had their solar panels cleaned by Martian dust devils? And if a rocket landing would get dust ‘in the gear’, just driving around is going to be problematic.
As far as mass, how much does all that motors, gears, and cables weigh? It better be pretty robust if they expect it to work. If they ditched all that and just had it land attached a rocket platform that detached on landing and flew away, wouldn’t that be a big mass saving?

– The panels are only partly cleaned. I assume dust on dust doesn’t stick as forcefully as on surfaces.*

– Yes, the dust gets into the bearings, which is perhaps why the wheels stick after a while. They construct a lot to protect against it, I think.

– The robust gear is mostly or all for free, I don’t know if they made it sturdier for landing. It it is needed to get the MSL traverse 6 km up if need be. (I.e. if the mission lasts long.)

————-
* Btw, the “spill the bean” link in my other comments have several talks on this. They are developing systems that removes dust from gear, as it is a major pain in the heat shield – one of the main Mars problems. With the perchlorates, it is also cancerogenous for human visitors.

Electrodynamic traveling waves are apparently a good balance between mass, energy needed and gear complexity.

Eseentially they do the MSL landing with some variations. But forget “the 7 minutes of terror”! This will be “the ultimate terror”.

– They use the same weight and steering thruster system to make guided flight for the same precision landing ellipse. But at a much shallower angle since the Dragon isn’t as aerodynamic.

– They are not using chutes. After achieving aboslute lift right before the finish, they drop the weights to go down. The radar have to pick up the ground and make a landing decision 4 s (IIRC) before hitting ground level at supersonic speeds. Then they do a full 2 ton propellant burn for a 9 g (IIRC) final brake manouver.

– The last 40 meters will be a gently landing. They won’t have propellant to get away from problems in the cheap “use the original Dragon” missions.

This approach will achieve parity with MSL and land 1 mt of payload up to the same 1 km below the Mars geode (MOLA) in the same precision landing ellipse, at the expense of using much more fuel. But with a cheap launcher like the Falcon Heavy, who cares? They can also land more than 1 mt, the meeting figures, at the 3 km below MOLA that they are initially interested in (Red Dragon, Ice Dragon)

If the Dragon is scaled up it can land any mass in the same way, likely higher up. The drawback? Hauling lots of fuel, facing “the ultimate terror”, take a 9 g kick in the pants. Some will probably go for it. [Musk volonteers/]

Like betting on a Royal Flush with only a King, Queen and Jack in your hand, this project is “ALL IN” during these seven minutes. I would be interested to know what thier internal odd makers give for a successful landing.

This seems so complex, with so many possible points of failure, so many ways to go wrong, that I think the odds against it landing safely are astronomical. But maybe they know something I don’t. Er, could be! I guess they thought it through.